Cam mechanism



Oct. 26, 1948. H KN S 2,452,372

CAM MECHANISM Filed Nov. 2, 1944 Inventor: Joseph R Harkness,

His Attor'he s.

Patented Oct. 26, 1948 CAM MECHANISM Joseph R. Harkness,. Schenectady,N. Y., assignor to General Electric Company, a corporation of New YorkApplication'November 2, 1944, Serial No. 561,568

(Cl. 7 i567) 2 Claims. 1

My inventionrelates to ignition'system circuit interrupters andparticularly to such devices'as are used withzmagnetos for supplyingignition to multi-bank engines.

An objectof my invention is to provide an improved ignition systemcircuit interrupter.

Another object of my invention is to provide an improved ignitioncircuit interrupter operable by a composite laminated cam for providingthe de sired circuit interruptions to a single set of breaker contactsfor providing ignition to all. of the cylinders-of all of the banks of amulti-bank engine;

Further objects and advantages of my invention will become apparent andmy invention will be better understood from the following descriptionreferring to the accompanying drawing, and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

In the drawing Fig. 1 is a plan View of a circuit interrupterincorporating an embodiment of my invention; Fig. 2 is an enlarged endview of the composite laminated cam shown in Fig. 1 mounted on a camshaft; Fig. 3 is a side view of the compositelaminated cam shown inFigs. 1 and 2; and Fig. 4 illustrates the end views of the two sides ofcam laminations forming the compositecam shown in Figs. 1, 2, and 3.

In ignition systemsprovided with magnetos as the source of electricalpower, one conventional circuit-interrupter arrangement includes a pairof circuit breakers each of which is operated to open the circuit whenthe current in the primary of themagneto reaches a maximum current valuein one direction of current flow. This has been found to resultinadefinite transfer of metal from one of the contactsof the breaker tothe other contact, resulting in a building up of one contact and awearing away of the other. This metal transfer is not the same aspitting which results from= arcing and sparking. between the contacts ofthe circut interrupter, and is not detrimental in the same sense as thepitting of the contacts, as; the spacing between the contacts tends toremain substantially the same until one of the contacts becomes. worn.away. However, this action is often misinterpreted by mechanics andmaintenance. men with the result: that breakers hav ing'contacts ofthistype are replaced when such replacement is not necessary. It isdesirable, therefore, that this condition should be eliminated orminimized and, therefore, I provide an improved circuit interrupter toovercome this undesirable condition.

Ihe drawing illustrates one embodiment of my invention in which anignition system circuit interrupter is adapted to interrupt the primarycircuit of an ignition system magneto for each maximum current conditionof the magneto primary winding for both directions of current flowthrough this winding. Furthermore, this single set of contacts isadapted to be operated by a single composite laminated cam. In multiplecylinder engines of the multi-bank type it becomes necessary to providea very large number of lobes onthe cam for operating such a circuitbreaker and it becomes increasingly difficult to manufacture a cam ofthis type and to maintain a reasonable small dimension for the diameterof the cam. There are a number of reasons for the impracticability ofmanufacturing a one-piece multiple cylinder cam of this type among whichis the difficulty encountered in grinding the lobe surfaces on the cam.As is well known in the grinding art, there is a maximum efficiency forthe surface speed of the grinder for manufacturing certain articles ofspecific materials, and if a cam is to be made with a large number oflobes the distance between adjacent lobes decreases directly with thedecrease in the size of the cam, and also with the number of lobes forthe cam. This results in a decreasing size of the grinding wheel forperforming the grinding operation in making the lobes on the cam andrequires thatthe grinding wheel be operated at a correspondinglyincreased speed in order to maintain the desired surface speed formanufacturing the cam. In my improved construction, the cam which isused tooperate the circuit breaker of my improved circuit interrupter isformed of multiple laminations arranged in sets, each of which isadapted to provide the desired circuit interruption for a correspondingbank of cylinders in a multi-bank engine. This type cam. could equallywell be used for an engine having a very large number of cylinders evenif the engine were notv of the multi-bank type. With such an arrangementitis possible to arrange the laminations of the cam such that the lobesof each set of laminations, or of each lamination if only onelaminationis used per set, are fixedly displaced a predetermined angulardistance or circumferentially spaced apart from. the lobes of the othersets of laminationsto operate the circuit breaker at the desired timingto provide the desired operation of the circuit breaker into circuitbreaking. position for providing the required circuit interruptionstoathe ignition system.

Referring to thedrawing, I have shown an em:- bodiment of my improvedignition system circuit interrupter adapted to be used With a twobankengine in which the circuit interrupter is provided with a circuitbreaker including a relatively stationary contact mounted on anadjustable supporting bracket 2 and a relatively movable contact 3mounted on an insulating operating crank i and electrically connected byconductor 5 to a terminal 6 which is insulated 3 from the stationarymounting bracket 2. The movable contact 3 is arranged to cooperate withthe stationary contact I for making and breaking the electrical circuitof the ignition system by operation of the crank 4 which is pivotallysupported by a pivotal mounting I. The crank 4 is provided with a crankarm 8 on which the movable contact 3 is mounted and with another crankarm 9 arranged with the end thereof formed as a cam follower biased intoengagement with the surface of a multi-lobe composite cam. This camcomprises a plurality of similar cam laminations Ii) and II fixedlymounted on a cam shaft l2 and retained against relative rotation thereonby a suitable key is arranged in a keyway on the cam shaft and incomplementary keyways in the cam laminations, and retained fixedly onthe cam shaft by a suitable nut M which threadedly engages the end ofthe cam shaft 2 for clamping the cam laminations between the nut and ashoulder IS on the cam shaft. In this construction the compositelaminated cam is formed of three laminations, however, any suitablenumber of laminations arranged in proper axial aligned sets may be usedto provide the desired number of lobes to the cam. The illustratedcircuit interrupter is adapted to be used with a two-bank engine,although it'might be equally applicable to an engine having the samenumber of cylinders arranged otherwise than as a two-bank engine. Thekeyway I6 is formed offset from a median between two lobes on thelaminations as shown in Fig. l, and by assembling adjacent laminationson the key l3, the outer two laminations ll! of the three camlaminations are arranged with the lobes thereof in aXial alignmentintermediate the lobes of the other intermediate inner cam laminationll. With this type arrangement, the alternate laminations are arrangedin axial alignment and in eifect form a single set of lobes, while thesingle intermediate lamination H forms another set of cam lobes. Thistype circuit interrupter is particularly adaptable for use with radialengines of the multi-bank type as all of the cam laminations may be madeidentical with the same compensation of the cam lobes for each of thelaminations if the piston rods of each bank of the engine are arrangedin the same order, and the desired angular displacement between adjacentsets of lobes can be provided by the proper location of the keyways inthe laminations as shown in Figs. 1, 2, and 3.

In order to provide the desired circuit interruption by the circuitbreaker contacts I and 3, the follower end of the crank arm 9 is made ofsuch a width as to span and engage the laminations of both sets of camlobes as shown in Fig. 3. By making the cam slightly longer axially thanthe cam follower, the proper operation of the circuit breaker isassured, and an even wear of the follower for both sets of cams willresult. If another bank of cylinders were to be used with this ignitionsystem, it would only be necessary to space the lobes of adjacent camlaminations to provide the desired circumferential spacing by 4 properlyoffsetting the keyway in the cam laminations, With this type arrangementit is possible to manufacture the cam laminations with a relativelylarge grinding wheel, thereby simplifying the method of manufacture andfurther assuring the desired accuracy for the spacing and compensationof the cam lobes of the cam, while retaining a relatively small camdiameter for operating a single breaker circuit interrupter.

While I have illustrated a particular embodiment of my invention,modifications thereof will occur to those skilled in the art. I desireit to be understood, however, that my invention is not to be limited tothe particular arrangement disclosed, and I intend in the appendedclaims to cover all modifications which do not depart from the spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A cam mechanism for actuating a periodically operated devicecomprising a rotatable cam shaft, a multi-lobe composite cam membercomprising three cam laminations fixedly mounted on said cam shaftadjacent each other with the lobes of the outer cam laminations arrangedin axial alignment and the lobes of the intermediate laminationscircumferentially spaced from the lobes of outer laminations, a singlecam follower having a member engaging and bridging all three of said camlaminations and means for biasing said cam follower into engagement withsaid cam member.

2. A cam mechanism for operating a periodic switch comprising arotatable cam shaft, a multilobe composite cam comprising an odd numberof similarly shaped cam laminations fixedly mounted on said shaftadjacent each other with the lobes of alternate laminations axiallyaligned and staggered relative to the lobes of the intermediatelamination, a pivotally mounted cam follower for actuating switchingmechanism, said cam follower having a cam-engaging portion bridging allof said cam laminations whereby said cam follower is actuated duringeach revolution of said shaft a number of times equal to a multiple ofthe lobes on each lamination, the alignment of the lobes of thealternate cam 1aminations acting to prevent the application of rockingtorques to said pivoted cam follower.

JOSEPH R. HARKNESS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,263,247 I-Ionold Apr. 16, 19181,322,319 McCutchen Nov. 18, 1919 2,025,191 Davis Dec. 24, 19352,303,771 Thomas Dec. 1, 1942 FOREIGN PATENTS Number Country Date392,454 France July 18, 1908

